The present invention is related to the subject matter of U.S. Patent application Ser. No. 622,054 now U.S. Pat. No. 4,113,998 filed on Oct. 14, 1975 and assigned to the same assignee as the present invention. That application is hereby incorporated by reference in the present application.
The present invention relates to computer test systems, and more particularly to a computer controlled system for performing a series of diagnostic test procedures on selected telephone subscriber lines extending from a central office.
In the service and maintenance of telephone system equipment, one important aspect is a rapid determination of the existence and location of problems directly related to the two-line subscriber telephone lines themselves. A telephone system central office has a large number, typically 10,000, "two wire" telephone lines extending to subscriber equipment. Each telephone line includes two wires, commonly referred to as "tip" and "ring", with a large number of these wire pairs being included in a cable having a cable jacket being connected to ground. At the central office, connections to a 50 volt battery provide enabling power on the line. In the United States, the average length of lines extending from the central office is 2.5 miles with the maximum length of approximately 10 miles.
One of the problems associated with maintenance service of the telephone lines lies in the relatively stringent requirements for maintaining the subscribers "on-line". If a faulty line is detected or reported and the fault cannot be located and serviced in a relatively short period, then the subscriber is usually re-connected to a new pair of wires in order to keep his equipment in service. When this is done, the previous pair of wires is abandoned. Consequently, after a period of time, cables typically have a large number of pairs of telephone wires which is only fractionally utilized. Increasing demand for telephone connections then require the very expensive project of laying new cables.
As would be expected, a great variety of approaches have been employed in an attempt to resolve this problem. Most such approaches have employed attempts at fault detection and location using test signals at frequencies in the range of voice frequencies, since these are the operating frequencies of the lines. One significant problem associated with the use of frequencies of this value in long line testing lies in the difficulty of making determinations of susceptance and conductance for the entire length of the line. Such measurements are needed to determine capacitative loading along the line. The resistive portion of the impedance increases with distance along the line, while the reactive portion decreases with distance along the line and for frequencies on the order of one kilohertz, these impedance values are approximately equal at a distance of 3 miles. Accordingly, this factor presents a limited distance for the determination of the characteristics of capacitive loading with a test frequency of 1 kilohertz. Additional problems arise from the necessity of protecting any measurement circuit from damage arising either from continuous direct low impedance connection to the battery through a short to the telephone wire connected to the battery, or from catastrophic high voltage, such as lightning striking the line when it is connected to the measurement circuit.
Furthermore, for many prior art test systems, the sheer mass of testing operations required for the large number of lines associated with each central office present a complex operating test procedure for the test station user. In order to improve the efficiency of these prior art test systems, central computers have been employed to perform testing algorithms on the various combinations of test results in order to determine which lines contain faults, as characterized by specific combinations of the measurement results. Such testing systems generally include means to store a data base for updated information concerning all of the lines emanating from a particular central office. This data base information would normally include length of the line, types of terminations and the types of equipment tied on to a line. Since many of these factors change fairly frequently, this data base is continually up-dated in the prior art test systems.
However, the test methods used for such systems and their implementation by the test systems are limited by the speed at which the tests can be performed, and the precision with which faults can be located so that correction may be achieved by a repairperson. Furthermore, the large data base which must be maintained requires a relatively high expenditure in order to provide the equipment necessary for storing and up-dating that data base. In addition, the data base storage portions of the prior art systems are configured so that a user must posses a relatively high skill level and to extract selected portions of the data base for display.
It is an object of the present invention to provide a system for testing telephone lines extending from one or more central offices whereby the lines are subjected to a series of diagnostic test routines to rapidly and economically determine both the existence and location of faults.
It is another object to provide a system for operation by a relatively unskilled operator wherein selected portions of a stored data base may be readily extracted.
It is a further object to provide a system for testing a large plurality of telephone lines extending from one or more central offices at a relatively high speed without requiring access to a data base generally representative of the previous condition of all the lined emanating from the central offices.
It is a further object of the present invention to provide a system for testing a large plurality of telephone lines emanating from one or more central offices wherein the plurality of a.c. and d.c. test signals are automatically applied in sequence to the lines, and the resultant test response signals are automatically processed in a corresponding sequence to detect the presence, character and location of faults and terminations.
It is still another object of the present invention to provide a test system for testing a large plurality of telephone lines extending from one or more central offices and for automatically diagnosing problems detected from the test measurements.